Apparatus and method for continuous pickling and regeneration of contact acid



Feb. 2, 1954 AND REGENERATION OF CONTACT ACID 5 Sheets-Sheet 1 Filed June 25, 1947 0 x Am A HM II 1 AN Qw A NM ww MN Ni N U M U c m W MW NN Q Q Feb. 2, 1954 MARTIN 2,668,130

APPARATUS AND METHOD FOR CONTINUOUS PICKLING AND REGENERATION OF CONTACT ACID Filed June 25, 1947 3 Sheets-Sheet 2 INVENTOR.

Feb. 2, 1954 E. D. MARTIN 2,668,130 APPARATUS AND METHQD FOR CONTINUOUS PICKLING AND REGENERATION OF CGNTACT ACID Filed June 25, 1947 3 Sheets-Sheet 5 Patented Feb. 2, 1954 APPARATUS AND METHOD FOR CONTINU- OUS PICKLING AND REGENERATION OF CONTACT ACID Edwin D. Martin, Chicago, Ill., assignor, by mesne assignments, to Koppers Company, Inc., Pittsburgh, Pa., a corporation of Delaware Application June 25, 1947, Serial No. 757,008

12 Claims.

The invention relates to an apparatus for and method of pickling iron and steel and for treating the spent pickle liquor so that it is regenerated and thus re-usable for pickling. l

The art of pickling has long been employed in the production of iron and steel. In fact, removal of scale from the metal by pickling has been known since very early times in the industry. In the practice of this art as commonly employed at the present time, several major problems exist. Thus, in present practice, pickling requires a longer time than is desirable, because the acid content of the spent pickle liquor must be reduced to a point where disposal of the waste liquor does not involve too great an economic loss. With such reduction in acid content, lack of uniformity of pickling On all parts of the metal is also encountered. Further, the quantity of spent pickle liquor, particularly at the larger steel mills, is so great that its disposal as Waste has been threatened with legislative action.

The general object of the invention is to provide a novel apparatus and method for Pickling metal and for regenerating the spent pickle liquor, which result in effective pickling of the metal and which substantially eliminate the problem of disposal of spent pickle liquor.

More specifically, it is an object to provide a novel apparatus and method for such pickling and regeneration of the pickle liquor, by which the regeneration of the liquor renders it highly effective for re-use in pickling and results in the production of a by-product of value, thereby eliminating the problem of the disposal of the liquor as a waste.

Another object is to provide a novel apparatus and method for picklin metal, which result in uniformity of pickling for all portions of the metal in a minimum of time.

A further object is to provide a novel apparatus and method for regenerating the spent pickle liquor, which make it economically practicable to maintain a relatively high acid content in the liquor for all of the pickling tanks, and do not require use of the liquor to a point where, to avoid excessive cost, its acid content is low.

Another general object is to provide an apparatus and method of the foregoing character, which make economic use of the heat employed in the method, which are simple to operate in that, to a great extent, it may be automatically controlled, and which require no great amount of change in the present type of equipment for 2 pickling and for the most part require only standard types of equipment for regenerating the spent liquor.

Other objects and advantages will be apparent from the following description taken in connection with the accompanyin drawings, in which:

Figure 1 illustrates diagrammatically the major elements of an apparatus embodying the features of the invention.

Fig. 2 is shown, as indcated, on two sheets of the drawings and is a diagrammatic illustration of such apparatus in a commercially practicable form, particularly adapted for use in a steel mill.

In pickling of iron and steel products, the process heretofore generally employed involved a solution or pickle liquor which required dumping the spent pickle liquor purely as a waste product. The acid content of such liquor when it was fresh would be in the neighborhood of 15% of sulphuric acid, but such liquor would be used until the acid content was reduced usually to the neighborhood of 5%. Below such acid content, the pickling was altogether too slow and unsatisfactory and above that point it was felt that there was an economic waste in dumping liquor of stronger acid content. Whilethe pickle liquor, during pickling, was maintained at a temperature above normal room temperature, since, it

was known that an elevated temperature increased the ability of the solution to remove the scale from the metal, there was no particular correlation between the acid content and the temperature of the liquor. In pickling of .iron and steel products, the oxides of iron forming the scale on the surface of the metal reacted with the acid in the liquor to form an iron sulphate. The sulphate formed was the ferrous sulphate heptahydrate. The heptahydrate when deposited in the pickle tanks, as frequently'occurred, gave considerable trouble in removing it. Thus, it formed a hard cake which could only be removed by chipping so that the liningsof the pickle tanks, which, of course, are acid resistant, would sufier from the damage resulting ,fromthe chipping operation. I The disposal of the spent liquor has also proved to involve several majorproblems. Thus, since there is no recovery of any useful product, the entire. cost of the pickling operation had to b e included in the cost of producing the steel. -Fur- I V thermore, because of the large volumes of pickle liquor used at the larger steel mills, pollution of streams and lakes'has resulted since such liquid waste products eventually find theirway to such bodies of water either through sewers or from direct dumping therein.

In the present instance, the pickling apparatus herein disclosed is of the type which is utilized in connection with the pickling of strip steel, such steel constituting a large part of the production of many large steel mills. Such steel, when it comes from the mills, is rolled into coils while hot, and such coilin necessarily results inra variation in the amount and character of scale produced on difierent parts of the strip. Thus, the edges and end portions of the strip, particularly the tail end portion, which forms the outer part of the roll, will carry a greater amount and different character of scale than the inner portions of the roll. The latter are protected from the oxidizing effect of the air and hav .a different rate of cooling because of the very fact that the steel is in the form of a coil, and the adjacent turns of the coil protect one another from the actionof the air except for the portions mentioned.

In pickling practice heretofore employed, such variations in the scale on'the strip resulted in a lack of uniformity of pickling throughout the strip, particularly with the lower acid content of the pickle liquor just before the liquor was dumped. If such strips were held in the pickle solution long enough to completely pickle the portions where scale of certain character existed, ovenpickling would occur in those portions where the scale was of different character so that the result was not entirely satisfactory.

Ihe present invention provides for a correlation between the acid content of the liquor and the temperature thereof so as to obtain an optimum rate of pickling which is substantially uniform for all portions of the strip. Furthermore, it has been found that by maintaining the acid content and temperature within a given range throughout the entire pickling process, not only can all portions of the steel be pickled to substantially the same degree in the same length of time, but also that such time is substantially shorter than was heretofore deemed necessary, particularly with the lower acid contents heretofore employed. To this end, it has been found that, if the pickle liquor is maintained at an acid concentration of at least 14% to 22% by volume of 10.0% sulphuric acid, and preferably between 16% and 20%, and if the pickle liquor throughout all picklin tanks is maintained at a temperature within the range of 180 to 220 .F., and preferably between 200 and 210 F., then such uniformity :of pickling of all parts of the metal in .a relatively short period of time is attained.

' Coupled with a pickling system controlled as to acid content and temperature as stated above, I provide regeneration apparatus to obtain from the spent pickle liquor asulp'hate in aform which is commercially valuable, namely, ferrous sulphate monohydrate. To do so, I maintain the liquor during the recovery process at an elevated temperature, which maybe substantially the same as that of the pickling bat-h so that there 'is a direct :saving in heat throughout the entire aptparatus. In other words, there is no intentional cooling of the liquor at any point in the system. While, of course, heathas to be added tothe liquid at some point to maintain such temperatures,

since they are above normal air temperature, such heat is held to a minimum by virtue .of other factors, such as preheating of the metal and use of warm water for washing or rinsing purposes so that the apparatus in its entirety, while maintaining the desired temperatures for the liquor throughout, necessitates supplying a minimum of heat to maintain such temperatures. The Warm water used in rinsing is also utilized at other points in the system so that any acid and sulphate removed by the rinse water is retained in the system.

Another important feature of the invention lies in the fact that it has been found that at the above-mentioned temperatures and acid strength of the pickle solution, the presence of sulphate in the pickle liquor .does not detrimentally affect or slow up the pickling operation. Preferably, the sulphate concentration in the pickle tanks is kept below the saturation point of the sulphate so that no difliculty arises from having to remove deposits .of the sulphate therefrom. Because of the complete re-use of the pickle liquor and the consequent elimination of any loss of acid, the acid added to the pickle solution durin regeneration need only'be chemically equivalent to the amount of sulphate producedduring pickling.

mentioned above, the ferrous sulphate produced is in the form of the monohydrate rather than the heptahydrate. This chiefly resultsfrom the use of the acid concentration and the temperatures maintained both in the pickling and recovery portions of the process. While I have stated the prefer-red range of such temperatures, reference in the specification and claims to temperatures as being in the neighborhood of 200 F. is intended to cover the broad range .heretc- :fore mentioned. Production of the monohydrate is obtained by precipitation thereof effected both by concentration of the spent pickle liquor with heat and by adding make-up acid to the liquor before such concentration, it being known that an increase in acid content of a pickle solution lowers the point of saturation for the sulphate. The addition of acid at this stage in the recovery process also has another benefit resulting from the fact that acid added to the solution produces heat. The monohydrate is a product which is commercially valuable and has a number of uses. Thus, the monohyd-rate may be .used as an ingredient of fertilizer, it may be readily used in the manufacture of .sulphuric acid, it is readily usable in making iron oxide pigments, it can be used inthe production of iron powder for powder metallurgy, or it maybe fed back into a sinter n plant for use in a blast furnace. With all these uses, it has a substantial monetary value and where, in the old systems, the spent pickle liquor was all waste, the present apparatus results in .no waste whatever.

Production of the monhydrate .rather than the .heptahydrate also provides attainment of certain other advantages. WVhile it is preferable that the liquor in the pickle tanks be kept at a point below the saturation point of the sulphate so that no deposit of the sulphate occurs in the pickle tanks, no difiiculty arises even if such deposit does occur since the monohydrate is easily broken up and, .in .fact, can be dissolved and washed away merely by the use of a warm water wash. The point of maximum solubility of the sulphate is at about F. Consequently, by maintaining the liquor in the neighborhood .of 200 throughout the entire system, as stated above, any cooling of the liquor that occurs in piping in the system merely increases the solubility of the sulphate so as to insure no deposits in such piping. .It is believed that the high temperature pickling, that is, pickling at the temperatures mentioned above, together with the acid concentration tend to result in production of the monohydrate rather than the heptahydrate. However, if the spent pickle liquor were cooled at any point in the recovery process below the temperature of 150 F. with not too high an acid concentration, the sulphate would take up water from the solution and the heptahydrate would be produced. In the present system, however, the use of temperatures in the neighborhood of 200 with the above-mentioned acid concentration not only in the pickle tanks but also throughout the entire regeneration process results in precipitation of the sulphate in the form of the monohydrate, and by removing the sulphate in this form and drying it before cooling, it will not revert to the heptahydrate form.

The apparatus illustrated in the drawings, particularly in Fig. 1, may be arranged so that a gravity feed of the liquor is utilized both throughout the pickling process and through the regeneration part. This simplifies the handling of the liquor since it need be pumped only at one point in the entire system. It has also been discovered that preheating of the metal prior to the pickling, to a temperature substantially above that of the pickle liquor, causes an action to take place when the metal is first immersed in the pickl liquor, that greatly facilitates the breaking up of the scale, so that the usual mechanical scale breaker heretofore frequently employed is no longer necessary. The pickling process also involves a treatment of the metal at an intermediate point in the pickling by a water spray to assist in the removal of red oxide from the metal, a form of scale which has heretofore caused considerable difficulty in its removal. The movement of the metal through the pickle tanks as well as the flow of liquor from one to another is concurrent and is believed to be the most satisfactory in obtaining uniform pickling and has certain engineering advantages.

As heretofore mentioned, the apparatus shown diagrammatically in Fig. 1 includes only the major elements thereof and particularly illustrates how the gravity feed of the pickle liquor may be utilized, not only in the pickling tanks, but also in the various parts of the regeneration process, with a pump placed at only one point in the entire system so that liquor will be fed by gravity through the complete circuit and back to the intake of the pump. In this figure, I have shown a plurality of pickle tanks, indicated respectively at It, II, I2 and I3. ,Four such pickle tanks have been shown for the reason that it has been found that this number of tanks is most convenient in pickling materials such as strip steel and is the number commonly employed. The steel which comes from the mill, as heretofore mentioned, is in rolls or coils, but such coils are unrolled and the strip passed continuously through the four pickle tanks, the rear end of each strip being connected to the lead end of the next strip by some means such as a seam weld which may be easily disposed of, if desired, by cutting out the seam after the pickling is completed. The flow of pickle liquor is concurrent with the movement of the steel through the pickle tanks and, to this end, pickle liquor is introduced into the tank it by means of an inlet pipe M. The liquor flows from one tank to the next by connections I5 so that gravity thereby produces the flow of the liquor.

From the last tank I 3, the liquor is withdrawn, and in this instance I place a pump it adjacent the last tank I 3 to withdraw, liquor therefrom as through a pipe I1. The pump l6 raises the level of the liquor as the latter enters the regenerative part of the apparatus so that gravity flow throughout the system is thereby attained.

Treatment of the spent liquor in the regenerative portion of the apparatus comprises generally mixing of fresh acid with the spent liquor, concentration of the liquor by evaporation to cause precipitation of the ferrous sulphate, settling of the liquor to separate the precipitate from the remaining liquor, and then dilution of the separated and concentrated liquor to the desired strength for pickling. The precipitated sulphate is removed when separated from the major portion of the remaining liquor and is passed to a filter, is washed and then dried. The liquor removed in the filter together with the wash water is conducted to the point where the liquor is diluted and, with the addition of water, the regenerated liquor is returned to the initial pickle tank I8 through the inlet pipe M. The regeneration apparatus may of course serve one or more pickling operations.

To disclose the regenerative process in somewhat more detail, in the embodiment shown in Fig. 1, the pump I6 discharges the spent liquor through a pipe 20 into a mixing tank 2I into which acid is also introduced through a pipe indicated at 22. The amount of acid added through the pipe 22, as heretofore stated, need only be the chemical equivalent of the amount of sulphate produced during the piclding operation in the tanks 19, II, 1 2 and I3. The introduction of the acid at this point has a number of advantages, among which is the fact that heat is added to the liquor by the reaction of the acid therewith. Furthermore, introduction of the acid at this point in the regenerative process lowers the saturation point for the sulphate and, consequently, tends to produce precipitation of sulphate crystals.

The mixing tank 2i is connected to a second tank 23 as by a siphon 24 where evaporation of a portion of the Water content of the liquor is effected. Such evaporation may be accomplished by the application of heat, although no specific means therefor is shown in the drawings. Concentration of the liquor as a result of such evaporation brings the liquor above the saturation point for the sulphate so that crystallization of the sulphate rapidly occurs in the tank 23.

.By constantly feeding the liquor from the mixing tank 2| to the crystallizing tank 23, a constant seeding of crystals occurs so that the crystal size may,'therefore, readily be controlled. The heat applied in the crystallizing tank 24 is also sufficient to maintain the desired temperature of the liquor for pickling. Such temperature, as heretofore stated, may range from to 220 F. and preferably is between 200 and 210 F.

From the crystallizing tank 23 the liquor together with the major portion of the sulphate crystals carried therein is discharged into a settling tank 25, preferably by means of a siphon 26. In the settling tank, the sulphate crystals settle to the bottom of the tank in the form of a slurry for withdrawal and further treatment, while the remaining liquor is decanted, as by means of an overflow pipe 21, to a dilution tank 36 where the liquor is diluted to the desired acid content for re-use in pickling.

The slurry containing the sulphate crystals, collecting in the bottom of the settling tank 25, is withdrawn through a pipe 3| and is discharged into a filter 32. Any sulphate crystals collecting in the bottom of the crystallizing tank 23 or mix-' fl in; tank may likewise be discharged through the pipe 13?! to the filter 3.2. The :filter 32 :'iS-0f a type which lprovides ior separation :of --the solid andsliquidzpcrtions-oi theslurry, and which also provides for washing-oi the solids and drying thereof. While several different types of standardfilters may be used, the filter shownat ii-2di- .agrammatically represents a rotary suction type of filter. Thus, the-slurry introduced into the -filter by means of the pipe 3i first separated into-crystals, which form the solid part of the slurry, and liquor. The crystals are then flash- -washed by 'cold water introduced into the filter through a pipe 33. The wash water and the filtered liquor are-discharged-from the filter through alpine a4 and arepumped to .-the=di'lution tank 30 tion tank 3'0 through a :pipe 31. The level of liquid in the entire system may Ice-easily controlled by a lioat '41) in the dilution tank. The diluted liquor, ready for re-use in the pickling portion of the apparatus, may be discharged to the first pickle tank 1'0 through the pipe l4 connected to a siphon in the dilution tank '38. An overflow pipe '41 may also beprovided from the dilution tank 30.

The sulphate separated from the liquor in the filter 32, after being washed by the water introduced into the filter, is quickly dried by the introduction into the filter at hot air through an inlet 38. By thus removing the moisture from the sulphate in the monohydrate form, there is no water present for 'the sulphate to revert to the heptahydrate. The sulphate thus remains in the monohydrate form after removal through a discharge 42, and can be easily handled without 1 'caking, where any reversion'to the heptahydrate would result in caking and consequent difiiculty in handling the material. The washing also eliminates any trace of acid and its consequent hygroscopic action so that the monohydrate,

which is non-hygroscopic, will not absorb moistime from the air.

As heretofore mentioned, the temperature of the liquor is maintained throughout the system in the neighborhood of 200 F. The heat for this purpose is derived chiefly from the heat supplied 'to the crystallizing tank 23 to evaporate a portion of the water content of the liquor. Some heat is also supplied by mixing the'acid with the liquor in the mixing tank 21. The total heat is sufficient to maintain the temperature in thisneighborhood. While the temperature may range 'from 180 to 220 R, the preferred range for the liquor in entering the first pickle tank is from 200 to 210 F. Some cooling of the liquor, of

course, occurs while the liquor passes through the various tanks, but preferably the flow is at such rate that the drop in temperature is not more than 10 F. between-the first and last pickle tanks. The spent liquor, in entering the mixing tank .2 I, of course, is immediately heated to some extent by the addition of acid, and the addition of heat for evaporation purposes in the crystallizing tank '23 obviously must-raise the temperature somewhat above the preferred range for r pickling to account or heat losses elsewhere.

Tlmstemperaturecf the liquor in theregen'eration portion of the apparatus, however, may be said to be within-the neighborhood of 200 F. The

slightly higher "temperature in the regeneration portion of the apparatus is, however, beneficial since the insolubility of the sulphate decreases with anincrease in temperature and, consequently, the higher temperatureaids in the precipitationof the sulphate crystals. Because of the temperature maintained'both in the regeneration portion of the apparatus and in the pickle tanks and because of the "acid concentration, the sulphate is :produced in the Imonohydrate form rather than the heptahydrate.

The apparatus shown in Fig. 2, disclosedbn two sheets of the "drawings, embodies all of the 'elementsshnwnini ig. 1. Fig. 2, however, shows the apparatus in a commercial practicable form particularly adapted for use in a steellmill in connection with "pickling of strip steel. While the various elements of the appa ratu's included in Fig. 2-are'not arranged in the drawings in such a way as to illustrate the gravity flow, as they are on one sheet, while th apparatus used in -r'egeneration of the liquor 'is shown'on the othershe'et, the connections between the two portions being clearly indicated.

into the first tank '56 through a line '53 and the liquor flows successively through the four tanks by connections connecting the tanks in series. The spent pickle liquor is removed from the last tank 53 through a pipe 55. The strip metal is adapted to be conducted through the four pickle tanks concurrently with the flow of liquor therethrough.

One of the features of the invention lies in the treatment of the metal prior to introduction into the'first pickle tank 50. Introduction of the metal at room temperature would, of course, tend to lower the temperature of the pickle liquor. It is, therefore, desirable, from that standpoint, to heat the metal to a temperature equal to or above that of the liquor in the tank 50. If the metal is heated to a temperature above such liquor, then additional heat is thereby added to the liquor and such addition, of course, is of advantage. However, an additional advantage can be obtained. which facilitates the initial removal of scale from the metal, if the metal is heated to a temperature substantially above that of th pickle liquor, so

facilitates loosening thereof and" speeds up the pickling. Preferably, with the pickle liquor in the neighborhood of 200 F., the metal is dryheated to a temperature of 240 to 250 F. by a heater indicated at Such temperature, of course, is above the boiling point of water and the action taking place may involve the formation of a layer of steam on the metal tending to break up the scale. The rapid contraction of the metal and scale due to the reduction in temperature may also be a factor in the action involved. However, whatever these factors are, the results obtained prove the merit of so heating the steel before introduction into the pickle liquor. Employment of such preheating of the metal eliminates the necessity of a mechanical scale breaker, although such a breaker may be used if desired.

' In the manufacture of steel, the red oxide of iron may be formed and included on the surface of the metal. Such red oxide has proved difficult to remove in ordinary pickling processes. In the present process, it has been found that spraying th metal with a warm water spray at some intermediate point in the passage of the metal from one pickle tank to another is helpful in effecting removal of the red oxide. Preferably, such warm water spray occurs at a point between the first and second pickle tanks 50 and 5!. In the present instance, such spray is indicated at 60 and the.

warm water drains off the metal into the first pickle tank 50. While introduction of such water would have a tendency to dilute the pickle liquor, the quantity thereof is relatively small so that it does not cause any great amount of dilution. The temperature of the water introduced by the spray 69 is preferably the same as or above the temperature of the pickle liquor so as to prevent any cooling of the latter.

Another feature of the invention lies in the treatment of the metal when it emerges from the last pickle tank 53. Such metal, of course, carries some pickle liquor with it as the metal is removed from the pickle tank and the liquor should, of course, be washed from the metal because of the acid content of the liquor. In the present apparatus, the metal is washed with warm water which is later used in the regeneration portion of the apparatus to dilute the regenerated liquor. Thus, all acid and sulphate removed from the metal by the wash water is retained in the system. The use of Warm water for washing purposes also is another factor in conservation of heatin the apparatus.

Specifically, the washing of the metal is divided into two parts to insure obtaining metal which is completely free of acid and sulphate. To this end, the metal, when it first emerges from the last pickle tank 53, passes under a spray 6| which sprays warm water on the surface of the metal and thus washes off the major portion of the adherent liquor. The spray water is collected in a tank 62 and is carried away by an outlet pipe 63. The metal, after passing under the spray 6|, then is immersed in warm water in a tank 64 to complete the washing or rinsing. By removal of the major portion of the liquor with the spray, the water in the immersion tank 64 is maintained at a relatively low acid and. sulphate content so that the metal when withdrawn from the rinse tank 64 may be'said to be completely freed of liquor. The water supplied by the spray El and the water in the rinse tank 64 is maintained at a temperature in the neighborhood of the metal, which, of course, is substantially the temperature of the pickle liquor, so that the metal, when it emerges from the rinse 10 tank 64, quickly dries in theairbecause of the difference in temperature between the metal andthe surrounding air. The water in the rinse tank 64 is constantly being replaced, an inlet 65' being provided for fresh water and the water being drained from the tank through a connection 68 with the spray 6 l.

- The spent liquor removed from the last pickle tank 53 through the pipe 56 is conducted to the regeneration portion of the apparatus shown on the second sheet of drawings for this figure. Inlets 10 may be provided in the line 56 to intro-' duce water therein for flushing purposes when necessary. The line 56 conducts'the liquor to a surge tank H, from which it is withdrawn by means of a pump 12 for discharge into a filter l3. The filter it removes any solids, such as scale, carried over from the pickle tanks by the line 56.

From thefilter'lB, the liquor is conducted by a line 14 to a mixing tank 15 in which sulphuric acid is added to the liquor. Thus, an acid storage tank 1-6 is provided and a pump 11, of suitable construction for handling acid, feeds acid into the mixing tank 15 where the acid is thoroughly mixed with the spent liquor. Mixtureof the acid with the liquor at this point in the regeneration process has several advantages, as heretofore mentioned. Thus, it creates heat in the liquor and reduces the point of saturation of the sulphate, facilitating precipitation of the sulphate at later stages in the regeneration process. Since no liquor is lost from the system, the quantity of sulphuric acid added in the mixing tank is just suffioient to make up for the amount of sulphate formed during the pickling process. As heretofore mentioned, the acid added is sulficient to establish an acid strength of 14% to 22% by volume of 100% sulphuric acid, and preferably 16% to 20%, when the liquor enters the first pickle tank.

From the mixing tank 75, the liquor with its increased acid content is forced by a pumpthrough a line 8| to a point in the apparatus where the liquor is concentrated by the evaporation of some of the water content thereof. In the present instance, such evaporation is elfected by discharging the liquor through a spray 82 located in a stream of hot gas. The hot gas may be supplied from a suitable furnace 83, shown in the drawings as being provided with a gas booster pump 84 and an air blower 85. The furnace 83 in the present instance is shown as a gas-burning type since coke oven gas is readily available at most steel mills and, therefore, is an economical fuel to employ. The hot gases generated in the furnace 83 are conducted to the point where the liquor is introduced through the spray 82, by means of a flue 86. In the specific apparatus herein shown, itis contemplated that the flue gases passing through the flue 86 will have a temperature in the neighborhood of 2000 To regulate the temperature of the flue gases to any point desired, an air by-pass 81 may be provided for introducing air from the blower directly into the flue 86. The heat obtained from the gases is not only sufiicient for evaporation, but also raises the temperature of the concentrated liquor so that its eventual return to the pickle tanks will be at the desired temperature.

From the spray 82, the liquor together with the flue gases may be conducted to a centrifugal evaporator 90 to separate the concentrated liquor from the flue gas carrying the evaporated moisture. Additional liquor may be introduced into the centrifugal evaporator 90 by means of sprays 1 l. il soas to obtain the greatest: benefit of the heat ot 'th'e gases." The moisture-carrying gases are then coriducted through a passage 92 to a, point where therinsewater collected in the outlet pipe 63 from the rinse tanks 62- and 64 of thepicklingapparatus in introduced into such gases by means of a spray 93 to-lower the temperature thereof. and condense a major portion of the entrainedmoisture. The rinse water together with the-condensate and cooled gases are then conducted to. an entrainment separator 94. The latter separates theg'as from the. liquid and the formeris carried through a passage 95 to a precipitator 96 in which any-acid remaining in the gas is removed. The acid, if of suificient quantity, may: be conducted-to the mixing tank I5 through a lineS'l.

The concentrated liquor separated: from the moisture-laden gases in the centrifugal evaporato'r. SIMS-drained therefrom through a pipe I66 into'afsettling tank IBI where the crystallized sulphate separates, in the. form of a slurry, from the? supernatant liquor. In order to prevent turbulence in the. contents of the Settling tank llltfthe pipe I discharges the concentrated liquorlinto a spillway I02 within the settling tank. and the liquor overflowsthe top of the spillyvayinto the main contents of the tank withoutistirringup the contents thereof. In the settlingtank II", the bulk of the settling ofthe sulphate crystals occurs within a few minutes. However, the capacity of the tank is such as to cause arelatively slow fiow therethrough so that liquorimaybepermitted to Settle up to two hours tothoroughly separate the crystals from the supernatant liquor. The presence of sulphate crystals inthe liquor in the settling tank has a seeding effectto. control the crystal size. The temperature of the liquor in the settling tank is smfiewhathigher than the liquor as it is withdrawn from the pickling tanksbecause ofthe heat-added from theiurnace 83. Such higher temperature, while in the neighborhood of 200 Fgof.-.course is beneficialin increasing the precipitation of. the sulphate since the saturation point for the sulphate above a temperature of; say, 150 I decreases. The elevated-temperature of-Tthe 'liquorinthesettling tank IIII also produces. a. moisture-laden atmosphere in the top th'ereoffand such atmosphere may be conducted through apipe I03 to the passage 92 which carriesrofith'e moisture-laden gases from the centrifugal 'evaporator 90+ To insure maintenance 01 the-liquor thetank IIII at'the desired tem perature, heatis preferably supplied to the liquor whilethesettling tank.- Thu's, hot gases may beintroduced into the liquor'in thesettling tank byiallinelfll extendingfrom the furnace 83. The liquorttherein may also be heated by steam coils Iflllwithin or encasing thetank IOI and supplied with superheated steam. The steam, of course, may be'drawn from-an outside source or may be generated in thefurnace 83, a water or wetsteam inlet I08 being shownfor the latter pur pose.

Theliquor in-the settling tank may also be recirculated 'throughthespray 82 and the centrifugal evaporator flli to secure greater concentrationand to obtain seeding of crystals, if desired. Tothis end, a pipe I05 extends from the tank IIlI with inlets either from the main portion of the tanker from the spillway I02,- and a pump Hit connected to the pipe I05and to the line 8| which conducts the liquor to the spray 82--w ill;thus recirculate the liquor through the latter.

The supernatant liquorresulting from: theset tling in the tank ml is withdrawn therefrom on dilution and re-use in the pickling tanks. To this end, the relatively clear supernatant liquor is decanted from the settling tank IUI through: a pipe III). and is conducted thereby to adilution tank I II. Water for diluting the concentrated liquor in the dilution tank III is preferably the water and condensate drainingfrom the entrainment separator 94, a drain pipe IIZ being pro vided for this purpose. Such water, as hereto! fore stated, is the rinse water thathas been-em ployed in the rinse tanks 621and 64? and has functioned to condense the vapor carried? over. into the entrainment separatorfrom the centrifL-L ugal evaporator The. water thus supplied through the pipe H2 isat the. desired tempera-- ture so that no loss of heat occurs. The: water passing through the pipe. I12, of course, carries; some acid and sulphate as a resultof. its function of rinsing the metal, but the contentthere of is so low that the water serves to dilute the. concentrated liquor withdrawn from the settlingtank IDI. Such dilution is controlled so .that the diluted liquor has the proper acid content and is reduced sufficiently in sulphate contentto' permit re-use in pickling. To providefor suchre-use, the supply-pipe filwhich. feeds'the regenerated liquor to; the first pickle-tank 50-: is connected to the dilution tank III to' receive liquor therefrom.

The sulphate precipitated by evaporation in the centrifugal evaporator 90' and precipitated in the settling tank IBI, of course, is the monohya drate because of the temperature and acidity-at which such precipitation occurs. The slurry containing the crystals of the monohydrate-col lects in the bottom of the settling. tank IOI and is discharged through a drainI I3 at the bottom thereof to afilter- II4. In this instance, the filter is illustratedas of the rotary disk type. In the filter I I I, the remaining liquor in the slurry is separated from the monohydrate crystals-and is drained therefrom through the drain H5. In order to insure complete removal of.the -liquor and acid from the crystals, the latter are washed with cold water suppliedby a; pipev IIBYin the filter. The acid, if any. were permitted to remain on the crystals, would have'a: hygroscopic action. By washingthe. crystals, substantially all such acid is removed .and the monohydrate-,- which is non-hygroscopic, will notabsorbany moisture from the air. The. wash water-used "at this point in .theesystenniscold; that lis substantially.at.room.temperature; because of the" factthat the monohydrate-is slowly solublein-water at this temperature- Thexvash-water mixes withthe liquor filtered from. the slurry and: passes;v out through. the: drain/ II5 along with the: liquor: The washed sulphate-is constantly removedfrom this filter I I4:- and --is discharged into -a-= dryerindicated generally at III, intqwhich-hot air is introduced, as at I20, to-quickly-dry the sul s. phate. This prevents-any moisturefrom'. the wash water from formingthe-h'eptahydrate and; consequently, no hard-caking-of the sulphate-occurs in-the dryer,- and the-sulphate in the monohydrate form can; therefore be=readily=-handled4 The liquor and wash water'carried by the drain I I 5-is discharged :intoa receiver I2-I from Whichit may be withdrawn by a pump 22 andcarried. to the-dilution-tank I I I throughapipe I23. The amount 4 oi;cold--=water employed id-washirig-thsulphate crystals inthe filter is so .smalIL that -it willfhave nomaterial tendency; to lower the tern-I perature of the liquor in the dilution tank I I I.- Vapor occurring in the receiver I2I may be carried through an exhaust pipe I24 to a condenser I25 with the condensate derived therefrom discharged by the pump I22 into the dilution tank III. Moisture-laden air from the condenser may be carried over into a vacuum type moisture trap I26, and the liquid collected therein is similarly drained by the pump I22 and discharged into the dilution tank II I.

From the foregoing description, it will be apparent that the apparatus and process herein described result in effective pickling of the metal and eliminate the problem heretofore existing of disposal of spent pickle liquor. By maintaining the temperature of the liquor substantially in the negihborhood of 200 F. with the desired acid concentration throughout the entire system, that is, both in the pickling portion of the apparatus and in the regeneration portion thereof, the desired character of pickling is attained, and in the regeneration of the liquor a valuable byproduct is produced. In addition to maintaining the temperature at the desired point, the acid content of the liquor is also controlled so that all parts of the metal are uniformly pickled in substantially the same time, which time is reduced to a minimum by the present process. By maintaining the temperature and acid content of the pickle liquor at the desired values, the presence of sulphate in the pickle liquor has no detrimental effect on the pickling operation. Consequently, the regeneration process need only reduce the sulphate content of the pickle liquor to such extent that the increase in sulphate content in the pickle tanks will not raise it above the saturation point. There is no intentional cooling of the liquor at any point in the process so that conservation of heat is a characteristic of the system and the system is, therefore, economical to operate in this respect. Furthermore, the re-use of the liquor and the saving of all sulphate derived in the system permit, from an economical standpoint, the use of a higher acid content for the liquor than has heretofore been deemed practicable.

I claim:

1. A continuous cyclic process for the pickling of iron and steel and for regenerating the used pickle liquor which comprises conducting the pickling operation with a pickle liquor having an acid concentration maintained within the range of from about 14% to about 22% by volume of sulfuric acid and maintaining the liquor at a temperature of from about 180 F. to about 220 F. whereby to permit rapid and uniform pickling at a relatively high ferrous sulfate concentration; continuously withdrawing used pickle liquor from the pickling step for regeneration and continuously concentrating the used liquor by evaporation; continuously adding fresh sulfuric acid to the pickle liquor being regenerated while at the same time maintaining the concentrated liquor at a temperature of from about 180 F. to about 220 F. whereby to effect rapid crystallization and precipitation of ferrous sulfate solely in the monohydrate form as a result of the combined effects of said temperature and increased acidity in lowering the solubility of ferrous sulfate monohydrate; continuously separating crystallized and precipitated ferrous sulfate monohydrate and thus obtaining a resultant concentrated liquor having a sulfuric acid concentration above said range; continuously diluting said resultant concentrated liquor.

with sufficient water to obtain a regenerated-- pickle liquor having an acid concentration within said range; maintaining the pickle liquor at :all times throughout the aforementioned regeneration steps at a temperature of from about F. to about 220 F. whereby to provide a regenerated, pickle liquor adapted for contin-,

2. The process of claim 1 further characterized in that said acid concentration in the pickling step is within the range of from about 16% to about 20% by volume of sulfuric acid.

3. A continuous cyclic process for the pickling of ferrous metal and for regenerating the used pickle liquor which comprises pickling the metal with a pickle liquor having an acid concentration maintained within the range of from about 14% to about 22% by volume of sulfuric acid and maintaining the liquor at a temperature of from about 180 F. to about 220 F. whereby to permit rapid and uniform pickling at a relatively high ferrous sulfate concentration; continuously removing the metal from the pickling step and rinsing the pickled metal with warm water to remove pickle liquor therefrom; continuously withdrawing used pickle liquor from the pickling step for regeneration and continuously regencrating the same by concentrating the liquor and crystallizing and precipitating ferrous sulfate monohydrate therefrom while maintaining the liquor at a temperature of from about 180 F. to about 220 F.; continuously adding fresh sulfuric acid to the pickle liquor during regeneration; continuously separating concentrated liquor from the precipitated ferrous sulfate monohydrate; continuously diluting said concentrated liquor with water including the effluent warm rinse water from the rinsing step whereby to obtain a regenerated pickle liquor having an acid concentration within said range and having a temperature of from about 180 F. to about 220 F.; and continuously recirculating the diluted pickle liquor to the pickling step without reheating thereby providing a continuous pickling and regeneration system wherein the heat of the rinse water assists in maintaining the temperature of the regenerated liquor during dilution thereof whereby to maintain the liquor at a temperature of from about 180 F. to about 220 F. substantially throughout the entire process.

4. A continuous cyclic process for the pickling of ferrous metal and for regenerating the used pickle liquor which comprises pickling the metal with a pickle liquor having an acid concentration maintained within the range of from about 14% to about 22% by volume of sulfuric acid and maintaining the liquor at a temperature of from about 180 F. to about 220 F. whereby to permit rapid and uniform pickling at a relatively high ferrous sulfate concentration; continuously removing the metal from the pickling step and rinsing the pickled metal with warmwater to remove pickle liquor therefrom; continuously withdrawing used pickle liquor from the pickling step for regeneration and continuously regenerating the same by contacting the used liquor t5 witlrliot'eases wherebii to concentrate the liquor by evaporation of 'water uiererrcm; continuous 1y "separating a coneent'r-ateti liquor from: efliuenfi gases; contimiouslyscrubbi'ngsaid effluent gases witli-the eilluent warm rinse water from the r-insingstep; crystallizing and precipitating ferrous-- sulfate monoliydrate from the concentratedliquor while maintaining the liquor at a; tern-- peratureof'fromabout I80 F' to about 22 F.-; contiirl'iously adding fresh sulfuric acid to the pickle liquor during regeneration; continuously separating concentrated liquor: from: the-- preci'p' itated' ferrous sulfate-monohydrate; continuous: 1y dilutingsaid concentrated liquor with water including the efiluent warm rinse wate'r from the scrubbing step wherebyto obtain 9:- regenerated: pick-le'liquor having an: acid concentration within -saidrange and liaving atemperatureof from about" 180 Fl toabout 220?" El; and continuously recirculating the diluted pickle liquor? to the pickling. step without reheating thereby providinga continuous pickling and regenerationsystem' wherein the-heat ofthe-rinse water assists in maintaining thetemperature of the regen erated liquor during dilutionthereof whereby to maintain the liquor ata temperature of from about 180 F toabout 2203 substantiallytl'irougliout tlie entire process; 7

5: A continuous cyclic-processior'the pickling of ferrous mei'fia'l and for regenerating the used pick-leliquor'whicli comprises pickling thekmetel with a: pickle liquor having an acid concerr tration maintained withinthe: range of" from about 14% to about 22% by volume of sulfuricacidland; maintaining the liquor at a tempera t'ureiof from about l b F; to-about 220 E". wherebyto'permit rapid and uniform pickling at a relatively higli ferrous sulfate concentration; continuously removing the metal from} thepickling step and rinsingthe piokled nietal with Warm Water: to remove pickle -liquor therefrom: continuously withdrawing: used pickle liquor from the picklingstep for regeneration and continuously" concentrating the used liquor by= evaporationend tlien crystallizing and precip itating. ferrous-sulfate monohydi'ate while main--- taming the-liquorat a; temperature of from about 189 F.- t'o about 220 FE;- continuou'sli adding fresh sulfuric a'cid' to the pickle liquor durin reg eneratiom continuously settling the concen-- tratedliquor' and continuouslyseparating a clear" supernatant liquon comprising a major portion off said concentrated liquorfrom a slurry con--- taining sa'id' fer'rous sulfate monohydr'ate and a" minor: portion 1 of said' concentrated.- liquor; coritinuouslfiseparatin g "solid ferrous sulfate mono hydrate from the liquor portionof said sl-urry-= and; combiningthe latter with said supernatant? liquor; continuously diluting the 7 combined liquors with water-including the effluent warm rinse water; from tl ieirinsing step whereby tech taina regenerated pickle liquor having an acicl concentration within saidrangeandhaving a"- temperature or frohi =about -1'80f- Fi'to about-228 131; and continuously recirculating" the dilutedpiclrla liquor: to the pick-ling step without re heating-thereby providing a-continuous picklingandu'egeneratiorrxsystem wherein tne heat ofth'e': rinseswaterzassists maintaining-x the tempera ture of... the: regenerated liquor during dilution thereoiewhereby, to maintain theiliquor, at a temk perature; of, from; about 1908 F; to.:- about;-2209 El substantially; throughoutz the; entire? process;

6 .A-,continuous-:process forzregeneratingusedv ,sult of the combined efiects of increased tern perature and increased acidity in loweringtlie solubility: of: ferrous sulfate monohydrate; con? tinuously recovering the crystallized and precip itateu: ferrous sulfate inonohydrat'e and separat'-' ing without further' removal of ferrous sulfate;

a;v concentrated liquor having asulfuric acid content greater than about 22% by volume; continuously" diluting the separated liquor with sum cient water to obtain a regenerated pickleliquor having? a pickling: concentration. of from"- about 1.4% to: about 22%- by volume of sulfuric: acid-i: ami maintainingxthe liquor at all' times'throu'g-htout the aforementioned' steps: at a temperature? w ithinitlie. range of *from about 180 F; to'abouti 2-20 F: whereby to provide at regenerated pickle? liquoradapted for use in pickling without re heating;

ii The: processof:- claim: 6! further characte1-;-' ized-irr'that a portion: of: the concentrated liquor is recycled from the crystallizing and precip'e itating' step to the evaporating: steps for seeding? the: used liquor duringevaporation" thereof;

8'1 A continuous processforl regenerating used sulfuric: aciu pickle liquor containing: ferrous sulfate and not less than about114%' by volume-' of" sulfuric: acid which comprises: continuously concentrating. the used liquor to; an; acid com oentr'ation greater than about-22%- by volume by' evaporation and. the addition of? fresh sulfuric acid; continuously maintaining: the?concentrated 3 liquor at'alte'mperature of'from-iabout 180? F: to. abouti22of F; whereby toiefiect rapid'crystalliza' tion and precipitation of? ferrous sulfate" solely asthemonohydrate andiin awcrystallineiform of settling rate; continuousljc'settling thecon centrated liquor and separating: a clearf super; natant liquor comprising a major portion ofsaid concentrated liquor from a -slurry: containingsaid ferrous sulfate monohydrateand'a minor portion of; the concentrated liquor; continuously sep'-- arating ferrous: sulfatemonohydratefrom the liquorportion of said'slurry; continuously combining: the latter with said supernatant liquor; and: continuouslydilutingithez combined liquors;

With suificient Water to obtain a: regenerated;

pickle liquor having: an acid concentration: of fronrabcutv l4-% to' about'22%; byrvolume of sulfuric acid;

9; A. continuous=process-r for regenerating used 1 sulfuric acid pickle? liquor containing ferrous? sulfate: and not" less than about 14 by' volume" of: sulfuric acid which: comprises continuously: concentratingthe used liquor to'.'an :acid concem' traitioni greater than: about: 22 by; volume-by;-

55 evaporation and the addition of fresh sulfuric:

acid; continuouslymaintaining the concentrated liquor at a-temperatureotfrom=about F; to: about 220 whereby: to=efiectrapidcrystallize tion? and precipitation of ferrous sulfate" solely: astheymcn'ohydrater and in a: crystalline form 0f; settling rate; continuously settling v the concentrated liquor andseparating a clear super;-

nataiit liquor comprisingv a major'portion OffSaid'i concentrated liquor fromxaslurry 'containing said:

sulfuric; acid; pickle: liquor containing-; fer-row 751: ferrous sulfatezmonohydratevand'amines-portions of the concentrated liquor; continuously separating ferrous sulfate monohydrate from the liquor portion of said slurry; continuously combining the latter with said supernatant liquor; continuously washing the separated ferrous sulfate monohydrate with water; and continuously diluting the combined liquors with water including the eflluent Wash water from said washing step whereby to obtain a regenerated pickle liquor having an acid concentration of from about 14% to about 22% by volume of sulfuric acid.

10. In a process forv regenerating used sulfuric acid pickle liquor by concentrating the liquor and precipitating crystalline ferrous sulfate monohydrate therefrom, the steps of separating the ferrous sulfate monohydrate crystals from the concentrated liquor, washing the separated crystals with water at substantially room temperature to remove adsorbed acid liquor therefrom without dissolving the crystals to any substantial extent, and immediately thereafter rapidly drying the washed crystals whereby to obtain acid-free non-hygroscopic crystals of ferrous sulfate monohydrate and whereby to avoid formation of ferrous sulfate heptahydrate and consequent caking thereof.

11. In apparatus for continuously pickling ferrous metal with sulfuric acid pickle liquor and for regenerating the used pickle liquor, the combination of a plurality of interconnected pickle tanks adapted to contain the pickle liquor, a rinse tank disposed adjacent the pickle tanks for rinsing the metal with water after pickling, an evaporator for concentrating the used pickle liquor to precipitate ferrous sulfate monohydrate therefrom, conduit means interconnecting said pickle tanks with said evaporator for supplying used pickle liquor from said pickle tanks to said evaporator, a settling tank having a direct fluid connection with the evaporator for separating the concentrated liquor from the precipitated ferrous sulfate monohydrate, a dilution tank having a conduit connecting the same with the upper portion of said settling tank for supplying supernatant concentrated liquor from the settling tank to the dilution tank, conduit means interconnecting said rinse tank and said dilution tank for supplying emuent rinse water from the rinse tank to said dilution tank and diluting the concentrated liquor with said rinse water, and conduit means interconnecting said dilution tank and said pickle tanks for recirculating the diluted liquor directly to said pickle tanks.

12. In apparatus for continuously pickling ferrous metal with sulfuric acid pickle liquor and 18 for regenerating the used pickle liquor, the combination of a plurality of interconnected pickle tanks adapted to contain the pickle liquor, a rinse tank disposed adjacent the pickle tanks for rinsing the metal with water after pickling, an evaporator for concentrating the used pickle liquor to precipitate ferrous sulfate monohydrate therefrom, means for supplying hot gases to said evaporator, conduit means interconnecting said pickle tanks with said evaporator for supplying used pickle liquor from said pickle tanks to the evaporator for contact with the hot gases, a settling tank having a direct fluid connection with the evaporator for separating the concentrated liquor from the precipitated ferrous sulfate monohydrate, a dilution tank having a conduit connecting the same with the upper portion of said settling tank for supplying supernatant concentrated liquor from the settling tank to the dilution tank, a. scrubber having a fluid connection with said evaporator for receiving efiiuent gases from the latter, conduit means connected to said rinse tank and to said scrubber for passing efliuent rinse water from the rinse tank to the scrubber for contact with the gases therein, a conduit interconnecting said scrubber and said dilution tank for supplying efiluent rinse water from the scrubber to said dilution tank for diluting the concentrated liquor with said rinse water, and conduit means interconnecting said dilution tank with said pickle tanks for recirculating the diluted liquor directly to said pickle tanks.

EDWIN D. MARTIN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,045,723 McFetridge Nov. 26, 1912 1,146,071 Hoffman July 13, 1915 1,865,607 Allen July 5, 1932 2,005,120 Whetzel et al June 18, 1935 2,017,773 Smith et al. Oct. 15, 1935 2,050,355 McCollam Aug. 11, 1936 2,078,088 Mantius et a1 Apr. 20, 1937 2,118,272 Smith May 24, 1938 2,155,854 Barnes Apr. 25, 1939 2,185,095 Smith et al Dec. 20, 1939 2,203,606 Whitfield June 4, 1940 2,322,134 Hodge June 15, 1943 2,372,599 Nachtman Mar. 27, 1945 2,379,823 Mottern Jan. 3, 1945 2,381,652 Dishauzi Aug. 7, 1945 2,541,901 Zademach et al Feb. 13, 1951 

1. A CONTINUOUS CYCLIC PROCESS FOR THE PICKLING OF IRON AND STEEL AND FOR REGENERATING THE USE PICKLE LIQUOR WHICH COMPRISES CONDUCTING THE PICKING OPERATION WITH A PICKLE LIQUOR HAVING AN ACID CONCENTRATION MAINTAINED WITHIN THE RANGE OF FROM ABOUT 14% TO ABOUT 22% BY VOLUME OF SULFURIC ACID AND MAINTAINING THE LIQUOR AT A TEMPERATURE OF FROM ABOUT 180* F. TO ABOUT 220* F. WHEREBY TO PERMIT RAPID AND UNIFORM PICKLING AT A RELATIVELY HIGH FERROUS SULFATE CONCENTRATION; CONTINUOUSLY WITHDRAWING USED PICKLE LIQUOR FROM THE PICKLING STEP FOR REGENERATION AND CONTINUOUSLY CONCENTRATING THE USE LIQUOR BY EVAPORATION; CONTINUOUSLY ADDING FRESH SULFURIC ACID TO THE PICKLE LIQUOR BEING REGENERATED WHILE AT THE SAME TIME MAINTAINING THE CONCENTRATED LIQUOR AT A TEMPERATURE OF FROM ABOUT 180* F. TO ABOUT 220* F. WHEREBY TO EFFECT RAPID CRYSTALLIZATION AND PRECIPITATION SULFATE SOLELY IN THE MONOHYDRATE FORM AS A RESULT OF THE COMBINED EFFECTS OF SAID TEMPERATURE AND INCREASED ACIDITY IN LOWERING THE SOLUBILITY OF FERROUS SULFATE MONHYDRATE; CONTINUOUSLY SEPARATING CRYSTALLIZED AND PRECIPITATED FERROUS SULFATE MONOHYDRATE AND THUS OBTAINING A RESULTANT CONCENTRATED LIQUOR HAVING A SULFURIC ACID CONCENTRATION ABOVE SAID RANGE; CONTINUOUSLY DILUTING SAID RESULTANT CONCENTRATED LIQUOR WITH SUFFICIENT WATER TO OBTAINED A REGENERATED PICKLE LIQUOR HAVING AN ACID CONCENTRATION WITHIN SAID RANGE; MAINTAINING THE PICKLE LIQUOR AT ALL TIMES THROUGHOUT THE AFOREMENTIONED REGENERATION STEPS AT A TEMPERATURE OF FROM ABOUT 180* F. TO ABOUR 220* F. WHEREBY TO PROVIDE A REGENERATED PICKLE LIQUOR ADAPTED FOR CONTINALL TIMES THROUGHOUT THE AFOREMENTIONED REREHEATING; AND CONTINUOUSLY RECIRCULATING THE REGENERATED PICKLE LIQUOR DIRECTLY TO THE PICKLING STEP WHEREBY TO PROVIDE A CONTINUOSLY RECICULATING THE AND REGENERATION SYSTEM CHARACTERIZED BY HIGH HEAT ECONOMY AND LOW HEAT INPUT REQUIREMENTS AS A RESULT OF THE MAINTENANCE OF SUBSTANTIALLY THE SAME OPERATING TEMPERATURE DUTING BOTH PICKLING AND REGENERATION. 